It is known that high combustion temperatures of an internal combustion engine result in the formation of oxides of nitrogen, NO.sub.x, which are discharged by the engine into the atmosphere. Water has been used as an anti-knock compound and to provide a cooling of the combustion process to reduce engine knock and to reduce formation of NO.sub.x. Devices that inject water into the air/fuel mixture of an internal combustion engine have not been widely used in commercial and passenger vehicles having reciprocating piston internal combustion engines. One drawback to the more general use of the water injection has been the inability to precisely control the amount of water introduced into the fuel mixture under varying engine operating conditions.
In the normally aspirated internal combustion engine having spark ignition, a fuel/air mixture is drawn into an intake manifold through a carburetor. The engine intake valves admit the air/fuel mixture to the cylinders at the proper time in the engine cycle. The amount of air/fuel mixture drawn into a cylinder on a single stroke of a piston is directly dependent upon the absolute pressure of the gas in the intake manifold. The amount of air/fuel mixture varies directly with the intake pressure in the manifold and inversely with absolute gas temperature. An effect of introducing water into the air/fuel mixture is that it cools the air/fuel mixture by evaporation. This results in more power per individual piston stroke of the engine.
The intake manifold gas pressure varies in a complex manner with engine speed and throttle opening. The suction or pumping rate of the engine is proportional to engine speed or engine rpm. The carburetor throttle valve is movable with the use of external linkages in the carburetor passage to vary the vaccum pressure in the intake manifold. In Applicant's fuel supply system the fluid, such as water, alcohol, and mixed water and alcohol, is introduced into the air/fuel mixture in a modulated manner that is proportional to engine speed times the absolute gas pressure in the intake manifold. The result is that the ratio of fluid to the air/fuel mixture remains relatively constant over the operating rpm of the engine.